Position determination method and navigation device

ABSTRACT

In the case of a position determination method, during traversal of a curve (K) the centroid (C d ) of the latter is determined from measured values of a direction sensor. The centroid (C m ) of the curve (K) of a digitized road ( 511 ) is determined from the alignment of road segments (S) of the digitized road which correspond to positions (P d ) determined by dead reckoning. The positions determined by dead reckoning are corrected on the basis of the difference between the determined curve centroids (C d ; C m ).

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application is a continuation of copending InternationalApplication No. PCT/DE01/01443 filed Apr. 12, 2001, which designates theUnited States.

BACKGROUND OF THE INVENTION

[0002] The invention relates to a position determination methodoperating by means of adjustment of a position determined by deadreckoning with the aid of a digital road map, and to a navigationdevice.

[0003] Patent specification U.S. Pat. No. 4,796,191 discloses correctinga position determined by dead reckoning by comparison with roads of adigital road map. For this purpose, a comparison is carried out betweena direction traveled by a vehicle and the direction of roads of adigital road map. As a result of adjusting with the aid of the digitalroad map, a summation of the measurement errors occurring in the sensorsis prevented.

[0004] Furthermore, a vehicle navigation system that uses dead reckoningand satellite navigation (GPS) for position determination is known frompatent U.S. Pat. No. 5,394,333. A position calculated by dead reckoningis plotted on a road map. A correction value for the GPS navigation isdetermined from the difference between the position on the road map anda position found by means of GPS.

[0005] However, position can be determined on the digital road map in aninformative way only in the event of a significant change in directionof the vehicle, for example during a turning-off maneuver.

SUMMARY OF THE INVENTION

[0006] It is an object of the invention to provide a positiondetermination method and a navigation device which can determine aprecise position on a digital road map even in the event of a slightchange in direction.

[0007] This aim is achieved by a position determination method operatingby means of adjustment of a position determined by dead reckoning withthe aid of a digital road map, comprising the following steps:

[0008] a succession of positions determined by dead reckoning is trackedon digitized roads of the digital road map and assigned to road segmentsof the digital road map,

[0009] during traversal of a curve the centroid of the curve isdetermined from measured values of a direction sensor,

[0010] the centroid of the curve of a digitized road is determined fromthe alignment of road segments of the digitized road which correspondsto the determined positions, and

[0011] the position determined by dead reckoning is corrected on thebasis of the difference between the determined curve centroids.

[0012] The centroid of the curve recorded in the digital road map can becalculated by weighting differences in the angles of consecutive roadsegments in their succession and adding them, and dividing the sum thusdetermined by the sum of the differences in the angles of theconsecutive road segments. The differences in the angles can bedetermined from shape points that define the road segments of the curve,and in that the differences in the angles are weighted with the timeinterval that has elapsed during tracking of the road segments on thedigital road map. The average speed during traversal of the curve isdetermined, and in that the time interval between the traversal of thecurve centroids is multiplied by the average speed in order to correctthe position, determined by dead reckoning, with the distance thusobtained.

[0013] Another position determination method according to the presentinvention comprises the steps:

[0014] tracking a plurality of positions by dead reckoning on digitizedroads of a digital road map and assigning the positions to road segmentsof the digital road map,

[0015] determining the centroid of a curve from measured values of adirection sensor while traveling along the curve,

[0016] determining a digital centroid of the curve of a digitized roadfrom the alignment of road segments of the digitized road whichcorresponds to the determined positions, and

[0017] correcting the position determined by dead reckoning on the basisof the difference between the determined curve centroid and digitalcurve centroid.

[0018] The centroid of the curve recorded in the digital road map can becalculated by weighting differences in the angles of consecutive roadsegments in their succession and adding them, and dividing the sum thusdetermined by the sum of the differences in the angles of theconsecutive road segments. The differences in the angles can bedetermined from shape points that define the road segments of the curve,and the differences in the angles can be weighted with the time intervalthat has elapsed during tracking of the road segments on the digitalroad map. The average speed during traversal of the curve can bedetermined, and the time interval between the traversal of the curvecentroids can be multiplied by the average speed in order to correct theposition, determined by dead reckoning, with the distance thus obtained.A curve can be defined in the digitized road by shape points. Thecentroid of the curve can also be determined by obtaining the individualchanges in direction from consecutive direction measurements and byweighting and adding the changes with the elapsed time and by dividingthe weighted and added changes by the sum of the measured changes indirection. The digital centroid of the curve recorded in the digitalroad map can be determined by weighting and adding the differences inthe angles of consecutive road segments in their succession with therespectively elapsed time which has elapsed during tracking of the roadsegments on the digital road map and by dividing the sum by the sum ofthe differences in the angles of the consecutive road segments.

[0019] An embodiment according to the present invention is a navigationdevice which comprises a distance sensor, a direction sensor, a mapmemory for a digital road map, and at least one processor for deadreckoning, which is connected to the distance sensor, the directionsensor and the map memory, which during traversal of a curve determinesthe centroid of the latter from measured values of the direction sensor,which determines the centroid of the curve of the digitized road fromthe alignment of road segments of a digitized road which corresponds tothe determined positions and which corrects the position determined bydead reckoning on the basis of the difference between the determinedcurve centroids.

[0020] The direction sensor can be a gyroscope. The navigation devicecan further comprise a satellite receiver for operating as a distanceand direction sensor and a display for displaying the determinedposition on the digitized map.

[0021] Centroids are determined for a curve that traverses a road andwhose course is determined by means of dead reckoning, and for acorresponding curve on a road of a digital road map. The curve centroidsare points which are also defined in the case of lengthy curves and areavailable for an adjustment of the position, measured by dead reckoning,with the aid of the digital road map. Such lengthy curves typically havea radius of 500 m to 1000 m.

[0022] A time measurement or a distance measurement can serve as a basisfor determining the curve centroids on the map.

[0023] If a time measurement serves as a basis for determining the curvecentroids, the average speed during traversal of the curve isadvantageously used for the position correction.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Further advantages, features and possible applications of theinvention emerge from the following description of exemplary embodimentsin conjunction with the drawings, in which:

[0025]FIG. 1 shows a vehicle navigation system,

[0026]FIG. 2 shows a curve recorded in a digital road map, and

[0027]FIG. 3 shows a curve centroid that was determined on the basis ofthe measured path, and a curve centroid that was determined on the basisof the corresponding curve of the digital road map.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028]FIG. 1 shows an autonomous navigation system 1 used in a motorvehicle. Said system has a computer or a processor 11 with a main memory12.

[0029] The processor 11 has access to a drive 2 for a map memory 21designed as a DVD (Digital Versatile Disk). A database in the form of adigital road map 51 is stored on this storage medium.

[0030] Furthermore, the processor 11 is connected to a distance sensor3, which is an odometer (tachometer), and to a direction sensor 4. Thedirection sensor 4 is a gyroscope.

[0031] The processor 11 is additionally connected to a satellitereceiver (not illustrated). The signals of said receiver are likewiseused for determining position. The satellite receiver can also take overthe task of the distance sensor 3 and the direction sensor 4 on its own.

[0032] The processor 11 calculates a vehicle position on the basis ofthe [lacuna] from the sensors and the map memory 21, and outputs saidposition to a display device 5 in the form of an arrow symbol. Thevehicle position is displayed on a digitized road 511 of the digitalroad map 51.

[0033] Illustrated in FIG. 2 is a lengthy curve K which is stored in thedigital road map and has a radius 750 m. This curve K is a segment of adigitized road that is defined by nodes. These nodes describe regularintersections and contain data on the distance and the direction to thenext node. Courses of curves are likewise defined by consecutive nodes.The latter are denoted in general as shape points.

[0034] The course of the curve illustrated is defined by the shapepoints N₀ to N_(n). A road segment S extends in each case between twonodes or shape points.

[0035] A plurality of vehicle positions during driving along the curveare entered on the curve K. Here P_(d) denotes a position determined bydead reckoning on the basis of distance measurements and directionmeasurements on the digital road map, and P_(m) denotes an actual, realposition that is initially unknown to the navigation device.

[0036] It follows from the illustration that the calculated position Pdis taken to be in front of the real position P_(m) because of a lengtherror. At a first instant, the two positions P_(d) and P_(m) are locatedon the road segment S between the shape points N₀ and N₁. At a secondinstant, the vehicle is still located in reality in the same roadsegment S while, according to the erroneous length measurement, thevehicle would already have described a curved course between the shapepoints N₁ and N₂. At the end of the curve K the vehicle is still locatedin reality on the curve, while according to the distance measured by thedistance meter the vehicle would already have had to leave the curve.

[0037] The course of the curve has no significant change in directionwithin a few meters, and so it is not possible to make a uniqueassignment of a point on the measured, traversed curve to a point on thedigitized curve of the digital road map. However, on the basis of acomparison between the changes in angle output by the direction sensorand the alignment of the road segments S, it is possible to establishwhether the position Pd calculated by the navigation device leads orlags the true position.

[0038] In order nevertheless to undertake a unique punctiform assignmentbetween the measured path and the digital road map, the curve centroidof the measured path is determined from the measured values of thesensors, and the curve centroid of the curve K recorded in the digitalroad map is determined from the alignment of the road segments S.

[0039]FIG. 3 shows a diagram in which there are plotted above a timeaxis the discrete changes in angle Δφ both in accordance with the sensormeasured values (white bars) and in accordance with a digital road map.Also plotted are the centroids C_(d) and C_(m) for the measured curveand for the digitized curve of the road map.

[0040] The curve centroid C_(d) of the traversed path is determined byvirtue of the fact that the individual changes in direction Δφ areobtained from consecutive direction measurements and in each caseweighted with the elapsed time t and added. This sum is then divided bythe sum of the measured changes in direction.

[0041] The centroid C_(m) of the curve recorded in the digital road mapis determined by virtue of the fact that the differences in the anglesΔφ of consecutive road segments are weighted in their succession withthe respectively elapsed time t which has elapsed during tracking of theroad segments on the digital road map. The values thus obtained areadded. This sum is divided by the sum of the differences in the anglesΔφ of the consecutive road segments.

[0042] It holds that:${C\quad d} = {{\frac{\sum\limits_{i = 0}^{n}{i*\left( {{\phi \quad d},{i + 1 - {\phi \quad d}},i} \right)}}{\sum\limits_{i = 0}^{n}\left( {{\phi \quad d},{i + 1 - {\phi \quad d}},i} \right)}\quad a\quad n\quad d\quad C\quad m} = \frac{\sum\limits_{i = 0}^{n}{i*\left( {{\phi \quad m},{i + 1 - {\phi \quad m}},i} \right)}}{\sum\limits_{i = 0}^{n}\left( {{\phi \quad m},{i + 1 - {\phi \quad m}},i} \right)}}$

[0043] in which case:

[0044] i is a discrete instant,

[0045] n is the number of the discrete instants (curve duration),

[0046] φ_(d,i) is the measured alignment of the vehicle at the instanti,

[0047] φ_(m,i) is the alignment of the road segment at the instant i,

[0048] C_(d) is the centroid of the curve traversed by the vehicle, and

[0049] C_(m) is the centroid of the curve of the digitized road.

[0050] The curve centroids Cd and Cm, which are instants, aresubsequently converted into a path difference or distance with the aidof which the distance measurement is corrected. Since the speed isfrequently not constant during a drive along a curve, use is made forthis purpose of an average speed. This is then multiplied by the timeinterval (C_(d)−C_(m)) between the curve centroids.

[0051] The path difference, that is to say the length error orcorrection value, can be calculated as follows:${{\delta \quad s} = {\left( {{C\quad d} - {C\quad m}} \right)*\frac{\sum\limits_{i = 1}^{n}{V\quad i}}{n}}},$

[0052] in which case

[0053] i is a discrete instant,

[0054] n is the number of the discrete instants (curve duration),

[0055] C_(d) is the centroid of the curve traversed by the vehicle,

[0056] C_(m) is the centroid of the curve of the digitized road,

[0057] V_(i) is the speed at the instant i, and

[0058] δ_(s) is the distance between the measured and the actualposition.

[0059] If, by contrast, the curve centroids are determined, on the basisof the traversed path measured by the distance sensor, the length erroris obtained directly from the difference between the curve centroids.

[0060] The calculated distance δ_(s) is divided into a plurality ofsections and successively added to or subtracted from the position P_(d)respectively calculated on the basis of the sensor data. As a result,the position P_(d) is gradually approximated to the actual positionP_(m), and a sudden change in the representation in the display deviceis avoided.

1. A position determination method operating by means of adjustment of aposition determined by dead reckoning with the aid of a digital roadmap, comprising the following steps: a succession of positionsdetermined by dead reckoning is tracked on digitized roads of thedigital road map and assigned to road segments of the digital road map,during traversal of a curve the centroid of the curve is determined frommeasured values of a direction sensor, the centroid of the curve of adigitized road is determined from the alignment of road segments of thedigitized road which corresponds to the determined positions, and theposition determined by dead reckoning is corrected on the basis of thedifference between the determined curve centroids.
 2. The method asclaimed in claim 1, wherein the centroid of the curve recorded in thedigital road map is calculated by weighting differences in the angles ofconsecutive road segments in their succession and adding them, anddividing the sum thus determined by the sum of the differences in theangles of the consecutive road segments.
 3. The method as claimed inclaim 1, wherein the differences in the angles are determined from shapepoints that define the road segments of the curve, and in that thedifferences in the angles are weighted with the time interval that haselapsed during tracking of the road segments on the digital road map. 4.The method as claimed in claim 1, wherein the average speed duringtraversal of the curve is determined, and in that the time intervalbetween the traversal of the curve centroids is multiplied by theaverage speed in order to correct the position, determined by deadreckoning, with the distance thus obtained.
 5. A position determinationmethod operating for a navigation system comprising the steps: trackinga plurality of positions by dead reckoning on digitized roads of adigital road map and assigning the positions to road segments of thedigital road map, determining the centroid of a curve from measuredvalues of a direction sensor while traveling along the curve,determining a digital centroid of the curve of a digitized road from thealignment of road segments of the digitized road which corresponds tothe determined positions, and correcting the position determined by deadreckoning on the basis of the difference between the determined curvecentroid and digital curve centroid.
 6. The method as claimed in claim5, wherein the centroid of the curve recorded in the digital road map iscalculated by weighting differences in the angles of consecutive roadsegments in their succession and adding them, and dividing the sum thusdetermined by the sum of the differences in the angles of theconsecutive road segments.
 7. The method as claimed in claim 5, whereinthe differences in the angles are determined from shape points thatdefine the road segments of the curve, and in that the differences inthe angles are weighted with the time interval that has elapsed duringtracking of the road segments on the digital road map.
 8. The method asclaimed in claim 5, wherein the average speed during traversal of thecurve is determined, and in that the time interval between the traversalof the curve centroids is multiplied by the average speed in order tocorrect the position, determined by dead reckoning, with the distancethus obtained.
 9. The method as claimed in claim 5, wherein a curve isdefined in the digitized road by shape points.
 10. The method as claimedin claim 5, wherein the centroid of the curve is determined by obtainingthe individual changes in direction from consecutive directionmeasurements and by weighting and adding the changes with the elapsedtime and by dividing the weighted and added changes by the sum of themeasured changes in direction.
 11. The method as claimed in claim 5,wherein the digital centroid of the curve recorded in the digital roadmap is determined by weighting and adding the differences in the anglesof consecutive road segments in their succession with the respectivelyelapsed time which has elapsed during tracking of the road segments onthe digital road map and by dividing the sum by the sum of thedifferences in the angles of the consecutive road segments.
 12. Anavigation device comprising: a distance sensor, a direction sensor, amap memory for a digital road map, and at least one processor for deadreckoning, which is connected to the distance sensor, the directionsensor and the map memory, which during traversal of a curve determinesthe centroid of the latter from measured values of the direction sensor,which determines the centroid of the curve of the digitized road fromthe alignment of road segments of a digitized road which corresponds tothe determined positions and which corrects the position determined bydead reckoning on the basis of the difference between the determinedcurve centroids.
 13. The navigation device as in claim 12, wherein thedirection sensor is a gyroscope.
 14. The navigation device as in claim12, further comprising a satellite receiver for operating as a distanceand direction sensor.
 15. The navigation device as in claim 12, furthercomprising a display for displaying the determined position on thedigitized map.